The endorsement marks Bush's fourth Senate endorsement and 30th total from a member of Congress.

"Jeb Bush is the proven leader the American people need as we face grave threats from abroad and continued economic challenges at home. Jeb is a serious leader with executive experience and a forward-looking vision," said Cochran, who's now in his seventh term in the Senate.

Bush also has support from Sens. Orrin Hatch of Utah, Dean Heller of Nevada, and Susan Collins of Maine. The Republican candidate, who now finds himself in the low-single digits in national polls, leads the GOP presidential field with Senate endorsements, falling just ahead of Sen. Marco Rubio who's backed by three of his colleagues.

Cochran narrowly survived a conservative primary challenge last year by Chris McDaniel. Despite heavy anti-Washington sentiment that rocketed McDaniel to tea party fame, Cochran won a closely-watched runoff in part thanks to Democratic voters who turned out in support of the pragmatic, incumbent senator.

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McDaniel has since endorsed Texas Sen. Ted Cruz.

The endorsement comes one day after Bush was in Cochran's home state for a fundraiser on Monday. Mississippi is one of several Southern states that will vote in the so-called SEC primary on March 1, when a large number of delegates in one single day will be up for grabs.

Bush was also there to attend a tailgate ahead of the University of Mississippi vs. Mississippi State football game in late November, and Bush's campaign rolled out a list of supporters from the state last week. Austin Barbour, the nephew of former Mississippi Gov. Haley Barbour, joined Bush's campaign in September after first running Rick Perry's super PAC.